In the past few weeks I have been having chest pains when I lay down. Pain is located at the base of my ribs, left of center, and over to under my left arm. As soon as I get up the pain subsides. The pain is not severe. As long as I am upright I have no pain. I have tried antacids without any relief. Iím not sure if this is stomach or heart related. All comments appreciated. Thanks.

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Keep moving, it makes it harder for the undertaker to catch you. Don

I would suspect it would be muscular, rather than heart or stomach? From my experience with angina, when I got up in the morning, the trend was no pain to pain in the left arm, shoulder region. Having a pain at the base of the ribs is not typical of angina. As for cessation of pain when you go from lying to standing, thats not typical either--you would expect the exact opposite of that.

donsabi,
It seems like a case of costochondritis to me. When you lie doown you are stretching your ribcage and pulling on one of the irritated ligaments...the pain can radiate to your arm.
I agree with ubie that it doesn't sound much like angina.